Axial flow turbomachines include an axially disposed engine core and a radially outwardly disposed engine case which surrounds the core. High bypass turbomachines also have a relatively large diameter fan case concentrically disposed radially outwardly of the engine core which shrouds one or more axially forward compressor fans. The radial distance between the core and the fan case varies with a particular engine configuration.
According to the prior art, a plurality of radially extending circumferentially arrayed fan case struts join together the fan case and engine core. These struts are configured to provide necessary structural support to the fan case which is subjected to a variety of structural and airflow induced axial, radial, and moment loads arising over a broad range of aircraft and engine operating conditions.
The fan case struts transmit these loads to the engine core. Various strut cross-sections may be used to provide necessary structural rigidity and strength. In addition, the fan case struts may have their exposed surfaces aerodynamically configured to provide shaped airflow benefits.
One such fan case strut, shown in U.S. Pat. No. 3,398,535, issued to Campbell, provides a mid-span annular structure concentrically disposed between the fan case and engine core which provides structural rigidity to the fan case strut-tied configuration. A plurality of radially extending circumferentially arranged fan case struts are structurally linked to this mid-span annulus. An additional plurality of V-struts further connect the mid-span annulus with the engine core at staggered intervals relative to the radially extending struts. The V-struts of this reference also include a pivotal connection on at least one strut end to avoid moment load transfer to the engine core.
Another fan case strut configuration, shown in U.S. Pat. No. 4,820,117, issued to Larrabee shows a one piece structural strut having an I beam shaped cross-section having lap-joined aerodynamic surfaces located at the strut's leading and trailing edges. These lap-joined aerodynamic contours provide only aerodynamic, not structural, benefits to this configuration.